The present invention relates to fragments of the insulin C-peptide and their use in the treatment of diabetes and diabetic complications.
Patients with insulin-dependent diabetes mellitus (IDDM), generally synonymous with type 1 diabetes, cannot survive without insulin therapy. IDDM is the classical, life-threatening form of diabetes, the treatment of which was revolutionized by the discovery of insulin in 1922. The prevalence of IDDM in Europe, North America and Japan is 0.25-0.4% of the population. There is a seasonal variation in the incidence of IDDM with more patients presenting in the autumn and winter months. The disorder affects a slight excess of males but this difference becomes less marked with increasing age.
The classical symptoms of IDDM in its acute phase are thirst, large urine volumes, fatigue and weight loss. Less frequent and minor symptoms are muscle cramps, skin infections and blurred vision. Nausea and vomiting may occur in advanced stages and denote impending ketoacidosis and coma. The duration of symptoms is short, usually 2-3 weeks or less. The patients present with high concentrations of glucose and ketone bodies in blood and urine while insulin levels are low or undetectable.
The etiology of IDDM is multifactorial but most likely includes a genetic predisposition for autoimmune reactivity together with environmental triggering, possibly via a virus infection, resulting in partial or complete destruction of the pancreatic beta cells. The destruction of beta cells may have been in progress during the 6-12 months preceding the onset of the disorder. In the acute phase of IDDM insulin deficiency is thus the dominating pathophysiological feature.
After starting insulin treatment many patients enjoy good blood glucose control with only small doses of insulin. There is an early phase, the xe2x80x9choneymoon periodxe2x80x9d, which may last a few months to a year and which probably reflects a partial recovery of beta cell function. This is, however, a temporary stage and ultimately, the progressive autoimmune destruction of the beta cells leads to increasing requirements for exogenous insulin.
While the short term effects of hypoinsulinemia in the acute phase of IDDM can be well controlled by insulin administration, the long term natural history of IDDM is darkened by the appearance in many patients of potentially serious complications. These include the specifically diabetic problems of nephropathy, retinopathy and neuropathy. These conditions are often referred to as microvascular complications even though microvascular alterations are not the only cause. Atherosclerotic disease of the large arteries, particularly the coronary arteries and the arteries of the lower extremities, may also occur.
Nephropathy develops in approximately 35% of IDDM patients particularly in male patients and in those with onset of the disease before the age of 15 years. The diabetic nephropathy is characterized by persistent albuminuria secondary to glomerular capillary damage, a progressive reduction of the glomerular filtration rate and eventually, end stage renal failure.
The prevalence of diabetic retinopathy is highest among young-onset IDDM patients and it increases with the duration of the disease. Proliferative retinopathy is generally present in about 25% of the patients after 15 years duration and in over 50% after 20 years. The earliest lesion of diabetic retinopathy is a thickening of the capillary basement membrane, there is then capillary dilatation and leakage and formation of microaneurysms. Subsequently, occlusion of retinal vessels occurs resulting in hypoperfusion of parts of the retina, oedema, bleeding and formation of new vessels as well as progressive loss of vision.
Diabetic neuropathy includes a wide variety of disturbances of somatic and autonomic nervous function. Sensory neuropathy may cause progressive loss of sensation or, alternatively, result in unpleasant sensations, often pain, in the legs or feet. Motor neuropathy is usually accompanied by muscle wasting and weakness. Nerve biopsies generally show axonal degeneration, demyelination and abnormalities of the vasa nervorum. Neurophysiological studies indicate reduced motor and sensory nerve conduction velocities. Autonomic neuropathy afflicts some 40% of the patients with IDDM of more than 15 years duration. It may evolve through defects in thermoregulation, impotence and bladder dysfunction followed by cardiovascular reflex abnormalities. Late manifestations may include generalized sweating disorders, postural hypotension, gastrointestinal problems and reduced awareness of hypoglycemia. The latter symptom has grave clinical implications.
Several theories have been advanced with regard to possible mechanism(s) involved in the pathogenesis of the different diabetic complications (1). Metabolic factors may be of importance and recent studies demonstrate that good metabolic control is accompanied by significantly reduced incidence of complications of all types (2). Nevertheless, after 7-10 years of good metabolic control as many as 15-25% of the patients show signs of beginning nephropathy, 10-25% have symptoms of retinopathy and 15-20% show delayed nerve conduction velocity indicating neuropathy. With longer duration of the disease the incidence of complications increases further.
C-peptide is a part of the proinsulin molecule which, in turn, is a precursor to insulin formed in the beta cells of the pancreas. Human C-peptide is a 31 amino acid peptide having the following sequence: EAEDLQVGQVELGGGPGAGSLQPLALEGSLQ (SED ID. NO. 1). It has been suggested in EP 132 769 that C-peptide may be given for the treatment of diabetes and in SE 460334 that insulin in combination with C-peptide can be administered in the treatment of diabetes and in the prevention of diabetic complications.
In recent years it has become apparent that type 1 diabetes is accompanied by consistently reduced activity of the enzyme Na+K+ATPase in several tissues, notably in renal glomeruli, retina, peripheral nerve, heart and skeletal muscle (3, 4, 5). Na+K+ATPase is an enzyme that is localized to the cell membrane and generates energy for transcellular transport of Na+ and K+ as well as for all co- or countertransported substrates in all mammalian cells. It is thus obvious that the activity of this enzyme is of fundamental importance for normal cell function. Deficient Na+K+ATPase activity in nervous tissue, glomeruli and retina is likely to be an important contributing factor in the pathogenesis of diabetic neuropathy, nephropathy and retinopathy. Na+K+ATPase activity is regulated via the Na+ concentration and by hormonal action; several hormones stimulate (thyroid hormone, noradrenalin, angiotensin, neuropeptide Y, insulin) or inhibit (dopamine, ANF) the enzyme""s activity (6). Despite insulin treatment sufficient to achieve good glycemic control, patients with type 1 diabetes show signs of insufficient Na+K+ATPase activity on a long term basis.
The present invention is based on the discovery of a group of peptides from the middle portion and the C-terminal part of the C-peptide molecule which are characterized by a remarkable ability to stimulate Na+K+ATPase activity. These peptides are all small fragments of the C-peptide molecule. C-peptide itself is able to stimulate Na+K+ATPase via activation of a G-protein, increase in the intracellular Ca2+ concentration and activation of protein phosphatase 2B (7). However, the smaller peptides"" stimulatory effect on Na+K+ATPase activity is similar to or greater than that of C-peptide itself. There is both in vitro and in vivo evidence to indicate that upon administration of one of these peptides together with regular insulin treatment, renal function improves, early signs of retinopathy regress and the function of somatic and autonomic nerves improves. Treatment with these specific peptides, optionally in combination with conventional insulin therapy is thus useful in preventing or substantially retarding the development of late diabetic complications. A potential advantage that the small peptides possess over C-peptide is that they may be administered orally instead of by injection as in the case of C-peptide and insulin.
In one aspect, the present invention thus provides a peptide being a fragment of the human insulin C-peptide, said peptide comprising the sequence ELGGGPGAG (SEQ ID NO. 2) (hereinafter xe2x80x9cpeptide Axe2x80x9d) or a fragment thereof, or the sequence EGSLQ (SED ID NO. 3) (hereinafter xe2x80x9cpeptide Exe2x80x9d), or a fragment thereof, and having the ability to stimulate Na+K+ATPase activity.
In a more particular embodiment, the present invention provides a peptide having the sequence ELGGGPGAG (SEQ ID NO. 2) or EGSLQ (SEQ ID NO. 3), or a fragment thereof.
Especially, the invention provides such peptides for use in therapy and more particularly for use in combatting diabetes and diabetic complications.
In another aspect the present invention provides a pharmaceutical composition comprising a peptide of the invention or a fragment thereof as hereinbefore defined together with at least one pharmaceutically acceptable carrier or excipient.
A yet further aspect of the present invention provides the use of a peptide of the invention, or a fragment thereof, as hereinbefore defined, in the manufacture of a medicament for combatting diabetes or diabetic complications.
As used herein the term xe2x80x9ccombattingxe2x80x9d includes both treatment and prophylaxis.
The present invention thus relates to the use of the following peptides which all are fragments of C-peptide: Peptide A (amino acid sequence ELGGGPGAG) (SEQ ID NO. 2) or components thereof, for example Peptide B (ELGG)(SEQ ID NO. 4), Peptide C (ELGGGP) (SEQ ID NO. 5) or Peptide D (GGPGA) (SEQ ID NO. 6). In addition, the invention includes Peptide E (EGSLQ)(SEQ ID NO. 3) and parts thereof, for example Peptide F (GSLQ) (SEQ ID NO. 7). All are intended for the manufacture of a medicament for treating type 1 diabetes.
Fragments of the invention have been proven to stimulate Na+K+ATPase activity to varying extent. Thus, studies involving renal tubule cells under in vitro conditions indicate that Peptides A-D stimulate Na+K+ATPase activity to an extent comparable to that for the whole C-peptide molecule. As much as 90% of the effect is achieved within 3 minutes. Moreover, Peptides E and F possess a stimulatory effect on Na+K+ATPase of renal cells which is comparable to or greater than that for the whole molecule. Combinations of Peptides A-D with Peptides E or F result in a stimulation of the enzyme activity that is greater than that for either peptide alone. For detailed examples of the stimulatory effects of the above peptides, see Example 1, below.
C-peptide exhibits specific binding to the surface of several cell types, notably renal tubule cells and fibroblasts. When fluorescently labelled C-peptide is incubated with cells it binds to the cell surface. The specificity of the binding is illustrated by the fact that preincubation with unmarked C-peptide prevents binding of the fluorescently labelled C-peptide. When preincubation with the fragments of the invention, particularly with either of fragments E or F was made, the fragments were found to prevent binding of the fluorescently marked C-peptide, demonstrating that the fragments bind specifically to the same binding site on the cell surface as C-peptide itself. For a detailed example of the binding of Fragment E see Example 28, below.
As mentioned above, included within the scope of the invention are peptides comprising the sequences of not only peptides A and E, but also their fragments. In the case of the nonapeptide A, such fragments may be 8 to 2 amino acids in length. In the case of the pentapeptide peptide E, such fragments may be 4 to 2 amino acids in length. Exemplary fragments B, C and D (for peptide A) and F (for peptide E) are listed above, but other fragments are also included.
In the case of peptide A certain studies on Na+K+ATPase activity, studying the ability of the peptide fragments to stimulate the activity of Na+K+ATPase of rat renal tubule segments, have shown that one or more of the central tri-glycine residues may be important, and preferred peptide fragments, where peptide A is concerned, thus include at least one, and more preferably, at least two, of the central tri-glycine residues. Thus, in addition to peptides B, C and D mentioned above, representative exemplary peptide fragments include GGGPGAG (SEQ ID NO. 8), GGGPG (SEQ ID No. 9), GGGP (SEQ ID NO. 10), GGP and GGPG (SEQ ID NO. 11).
Furthermore, it has been found that peptides containing non-natural D-amino acid isomers may also be active, including for example the dipeptide D-LG or D,L-LG. Thus, included within the scope of the invention are xe2x80x9cnon-nativexe2x80x9d isomers of the xe2x80x9cnativexe2x80x9d L-amino acid C-peptide sequences. Insofar as peptide A is concerned, it is believed that the presence of at least one (if D-peptide) or two (if L-peptide) of the central tri-glycine residues may be important in a 9 amino acid or less peptide segment.
In the case of peptide E, exemplary representative fragments include not only the tetrapeptide, peptide F, but also SLQ and LQ. The C-terminal Q residue is believed to be of importance. Likewise, non-native isomers or derivatives of the peptides e.g. peptides including D-amino acids are included within the scope of the invention.
The invention encompasses peptides comprising the sequences of peptides A and E. Thus, also included within the scope of the invention are peptides having N- and/or C-terminal extensions, or flanking sequences, to the sequences of peptides A and C. Such peptides may include additional amino acids which may either be those provided in the corresponding position in the native human insulion C-peptide or other amino acids (excluding of course the possibility of reconstituting the entire insulin C-peptide). The length of such xe2x80x9cextendedxe2x80x9d peptides may vary, but preferably the peptides of the invention are no more than 25 or 20, especially preferably not more than 15 or 10 amino acids in length. Exemplary peptides include octa-, hepta and hexa-peptides including the sequence of peptide E, e.g. LALEGSLQ (SEQ ID NO. 12), ALEGSLQ (SEQ ID NO. 13) and LEGSLQ (SEQ ID NO. 14).
The peptides of the invention can be used for the treatment of diabetes and diabetic complications, most notably type 1 diabetes and its complications. As used herein the term xe2x80x9cdiabetic complicationsxe2x80x9d thus includes all complications known in the art to be associated with various forms of diabetes. Whilst not wishing to be bound by theory, the utility of the peptides is believed, as explained above, to be linked to their ability to stimulate Na+K+ATPase activity. A further aspect of the invention thus includes the peptides for use in, and their use in preparing medicaments for use in stimulating Na+K+ATPase activity in a subject.
Na+K+ATPase activity may readily be assayed using techniques known in the art and described in the literature and thus the effect of the peptides in stimulating Na+K+ATPase activity may readily be determined (for example, see reference 7).
Thus, the peptides can be used for the manufacture of a medicament for stimulation of Na+K+ATPase activity, for treating type 1 diabetes patients with retinopathy, for treating type 1 diabetes patients with nephropathy, for treating type 1 diabetes patients with neuropathy and for retarding the development of late diabetic complications. The medicament may comprise insulin. The invention also relates to the method for treatment or prevention of the above given indications.
The peptides of the invention may be used singly or in combination and thus a pharmaceutical composition or medicament may be prepared comprising one or more of the peptides. As mentioned above, a synergy has been observed between peptide A or peptides based on or derived from peptide A (the xe2x80x9cpeptide A groupxe2x80x9d) and peptide E or peptides based on or derived from peptide E (the xe2x80x9cpeptide E groupxe2x80x9d). Thus, synergistic combinations of a peptide from the peptide A group, with a peptide from the peptide E group represent a preferred embodiment of the invention.
The peptides may also be used in combination or conjunction with other agents active or effective to treat diabetes and/or its complications. Such other active agents include for exammple insulin. In such xe2x80x9ccombinationxe2x80x9d therapies the peptide(s) and second active agent may be administered together in the same composition or separately in separate compositions, simultaneously or sequentially.
A further aspect of the invention thus provides a product containing a peptide of the invention, or a fragment thereof, as hereinbefore defined together with a further active agent effective to combat diabetes or diabetic complications, as a combined preparation for simultaneous, separate or sequential use in combatting diabetes and/or diabetic complications. Preferably such a further active agent is insulin.
In such combined therapies, where insulin is used, it is to be understood that the term xe2x80x9cinsulinxe2x80x9d encompasses all forms, types and derivatives of insulin which may be used for therapy e.g. synthetic, modified, or truncated variants of the active human insulin sequence.
The compositions of the invention may be administered orally or parenterally by the subcutaneous, intramuscular or intravenous route. The compositions of this invention comprise active fragments/peptides of the C-peptide molecule (e.g. Peptides A-F), together with a L pharmaceutically acceptable carrier therefor and optionally, other therapeutic ingredients, for example human insulin. The total amount of active ingredients in the composition varies from 99.99 to 0.01 percent of weight. The carrier must be acceptable in the sense that it is compatible with other components of the composition and is not deleterious to the recipient thereof.
The compositions may be formulated according to techniques and procedures well known in the art and widely described in the literature, and may comprise any of the known carriers, diluents or excipients. Thus, for example, compositions of this invention suitable for parenteral administration conveniently comprise sterile aqueous solutions and/or suspensions of the pharmaceutically active ingredients (e.g. Peptides A-F) preferably made isotonic with the blood of the recipient, generally using sodium chloride, glycerin, glucose, mannitol, sorbitol, and the like. In addition, the compositions may contain any of a number of adjuvants, such as buffers, preservatives, dispersing agents, agents that promote rapid onset of action or prolonged duration of action and the like.
Compositions of this invention suitable for oral administration may, for example, comprise active fragments/peptides of the C-peptide molecule (e.g. Peptides A-F) in sterile purified stock powder form preferably covered by an envelope or envelopes (enterocapsule) protecting from degradation (decarboxylation or hydrolysis) of the active peptides in the stomach and thereby enabling absorption of these substances from the gingiva or in the small intestine. The envelope(s) may contain any of a number of adjuvants such as buffers, preservative agents, agents that promote prolonged or rapid release giving an optimal bioavailability of the compositions in this invention, and the like.
In addition, the present invention relates to non-peptide compounds showing the same stimulatory effects as displayed by their C-peptide-derived counterparts. Such peptidomimetics or xe2x80x9csmall-moleculesxe2x80x9d capable of mimicking the activity of the naturally occurring proteins or peptides are likely to be better suited for e.g. oral delivery due to their increased chemical stability (8,9).
It is now commonplace in the art to replace peptide or protein-based active agents e.g. therapeutic peptides with such peptidomimetics having functionally-equivalent activity. Various molecular libraries and combinatorial chemistry techiques exist and are available to facilitate the identification, selection and/or synthesis of such compounds using standard techniques (10). Such standard techniques may be used to obtain the peptidomimetic compounds according to the present invention, namely peptidomimetic organic compounds which show substantially similar or the same activation of Na+K+ATPase and/or cellular binding characteristics as the peptides of the invention, e.g. as described herein in the Examples.
A further aspect of the invention thus provides a biomimetic organic compound based on the peptides of the invention, characterised in that said compound exhibits activation of Na+K+ATPase and/or cellular binding characteristics to renal tubule cells and fibroblasts at at least the level exhibited by the peptides and peptide fragments of the invention as hereinbefore defined.